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Question Number 93963 by  M±th+et+s last updated on 16/May/20

we have for quadratic equations  x=((−b±(√(b^2 −4ac)))/(2a))  what about cubic equation is there any  rules or ways to solve?

wehaveforquadraticequationsx=b±b24ac2awhataboutcubicequationisthereanyrulesorwaystosolve?

Commented by Kunal12588 last updated on 16/May/20

for the roots I heard there is a formula for  cubic too but it is too long to be remembered.  same for biquadratic.[don′t know for higher]  but there are methods to solve like cardano and  trigonometric [I heard of Farrari too, I think  it′s for biquadratic]

fortherootsIheardthereisaformulaforcubictoobutitistoolongtoberemembered.sameforbiquadratic.[dontknowforhigher]buttherearemethodstosolvelikecardanoandtrigonometric[IheardofFarraritoo,Ithinkitsforbiquadratic]

Commented by mr W last updated on 16/May/20

see Q89687

seeQ89687

Commented by mr W last updated on 16/May/20

once i made following summary for  cubic equation:

onceimadefollowingsummaryforcubicequation:

Commented by mr W last updated on 16/May/20

Commented by  M±th+et+s last updated on 16/May/20

thank you sir

thankyousir

Commented by Tony Lin last updated on 16/May/20

Commented by Tony Lin last updated on 16/May/20

Commented by Tony Lin last updated on 16/May/20

Commented by Tony Lin last updated on 16/May/20

we still can get the formula of cubic  and biquadratic in terms of a,b,c,d,e  but they are too hard to remember ,  which is totally not useful

westillcangettheformulaofcubicandbiquadraticintermsofa,b,c,d,ebuttheyaretoohardtoremember,whichistotallynotuseful

Commented by  M±th+et+s last updated on 16/May/20

thank you sir

thankyousir

Commented by  M±th+et+s last updated on 16/May/20

sir MR.W can you put an example for this rule  and thank you again

sirMR.Wcanyouputanexampleforthisruleandthankyouagain

Commented by mr W last updated on 16/May/20

you can apply the formulae directly   for any cubic equation, i don′t think  you need an example. but i give an  example:  x^3 −3x−4=0  p=−1, q=−2  p^3 +q^2 =−1+4=3>0 ⇒one real root  x=(((√3)+2))^(1/3) −(((√3)−2))^(1/3) ≈2.1958

youcanapplytheformulaedirectlyforanycubicequation,idontthinkyouneedanexample.butigiveanexample:x33x4=0p=1,q=2p3+q2=1+4=3>0onerealrootx=3+233232.1958

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